1. Field of the Invention
The present invention relates to an ultrasonic sensor including multiple sensor elements arranged in an array.
2. Description of Related Art
An ultrasonic sensor that has multiple sensor elements arranged in an array has been known. Such an ultrasonic sensor is used for measuring a location of an obstacle existing forward of the ultrasonic sensor, and used for sensing a shape of the obstacle. Also, an ultrasonic transducer for obtaining an ultrasound image has been known in, for example, a medical field. When this type of an ultrasonic sensor measures a location and a shape of an obstacle, it is typically required to obtain a time interval between transmission and reception of the ultrasonic wave. Further, it is required to obtain a difference in time or phase between the ultrasonic wave received by one sensor element and that received by another sensor element.
In the ultrasonic sensor, the positioning accuracy of the sensor elements influences accuracy for detecting the difference in the time or phase of the ultrasonic wave. It is therefore important to improve the positioning accuracy of the sensor elements. Japanese Patent Application Publication 2003-235098 corresponding to U.S. Pat. No. 7,309,948 discloses an ultrasonic sensor, in which a fixation member made of hard resin plays a role in positioning a transducer.
In the ultrasonic sensor disclosed in Japanese Patent Application Publication 2003-235098, since the fixation member is made of hard material, the fixation member restrains vibrations of the transducer, and as a result, sensitivity for detection of the ultrasonic wave is lowered. Regarding an ultrasonic sensor for monitoring a space around a vehicle, the ultrasonic sensor typically employs an ultrasonic wave with low frequencies. In this case, the ultrasonic wave has a large amplitude, and a hard fixation member causes an ultrasonic wave to be damped remarkably. Further, the hard fixation member can conduct vibrations from one transducer to another transducer, resulting in a worse cross-talk characteristic.